# How to solve practical OPAMP with finite differential resistance and finite offset current while other parameters can be considered ideal?

simulate this circuit – Schematic created using CircuitLab

Ip(bias)=200nA rd=differential resistance=5Mohm a=infinite What should be its output? I am confused if I should consider negative feedback and consider bias current gives only input offset voltage of straightway say that OPAMP is saturated.

• Assume Vin- = Vin+ =0 (ignore Ip*100=20uV) and Vout drives Vin to that voltage, so what is Vout ... Note R's are equal – Sunnyskyguy EE75 Mar 2 at 6:52
• How can I ignore 1V (200nA*5M=1V) – Buzz bee Mar 2 at 7:16
• So in a nutshell, in ideal case when input bias current $I_b = 0$ and also input impedance $Z_{in} = \infty$, you understand that the $V_{out} = V_{in} = -1V$. What do you want to ask that how to derive the value of $V_{out}$ if $I_b \ne 0$ and $Z_{in} \ne \infty$ right? – Unknown123 Mar 2 at 10:59
• @Unknown123 right – Buzz bee Mar 2 at 11:19
• You add additional voltage sources to the schematic, with the new voltages being the error voltages. You may need to perform Norton to Thevenin conversions. – analogsystemsrf Mar 2 at 13:36